OBJECTIVES: 1. To study Tag-negative revertant cell lines isolated from Tag-positive transformed lines carrying one copy of SV40 DNA in order to shed light on the regulation of expression of the SV40 A gene. 2. To examine skin fibroblasts from persons at high risk for cancer, to determine the generality of our observation that actin distribution is defective in skin fibroblasts from persons with the gene for adenopolyposis of the colon and rectum.